Battery, alternator, or ???

[astrowolf67]

1986 BII XLT 2.9 auto

Symptoms: When driving at night, everything is good till the rpm's drop when I slow down. My headlights get dim, and the turn signals blink slower than normal. It stay's running just fine, although it idles a bit low. It doesn't matter if I have the radio on or off, same with heater blower. I can shut it off, come back out cold or hot, and, it starts right up. I am not sure how old the battery is, as it was on the truck when I got it last fall. However, since it starts with out any trouble, I'm guessing the battery is just fine. Any suggestions?

Thanks,
David

[drofman]

Idle too low may be?

[astrowolf67]

Thought about that, but, went out and checked. It idles up when everything gets turned off. I plan to drive it to work tomorrow, so, I'll stop by Autozone on the way home and have them check the battery and alternator for me.

David

[astrowolf67]

Okay, I stopped on the way home from work, and had my battery and alternator tested. Battery had a charge of 13.6 volts, alternator was putting out between 14.5 and 15.6 volts. This shouldn't be what causes them to go dim should it? And, when I say dim, I mean it's a good thing I'm not moving cause I can't see kind of dim.

David

[drofman]

I'm not a tune up tech but may be the TPS out of range. Do you have a tach and if you do whats the idle at with lights on?